Sizing up a dinosaur

This exercise is a part of Educator Guide: A Tiny Dino and Iron Rain / View Guide

Editor’s note: On July 22, 2020, Nature retracted the study described in this article at the authors’ request. “Although the description of Oculudentavis khaungraae remains accurate, a new unpublished specimen casts doubts upon our hypothesis regarding the phylogenetic position” of Oculudentavis, paleontologist Jingmai O’Connor and her colleagues write in the retraction. A recent study posted at bioRxiv.org, a preprint server for studies that have yet to be peer-reviewed, examined the skull of Oculudentavis and suggested that it is not a dinosaur, but a lizard. In an e-mail to Science News, O’Connor notes that the unpublished specimen mentioned in the retraction — analyzed by a different team of scientists who, she says, have identified it as a lizard — does strongly resemble Oculudentavis. She concedes that Oculudentavis was also probably a lizard, albeit “a really weird animal and an important discovery, regardless of whether it’s a weird bird or a weird lizard with a bird head.”

Directions for teachers: After your students read “This ancient dinosaur was no bigger than a hummingbird,” ask them to answer the following questions.

1. What is Oculudentavis khaungraae? Why does the story refer to the creature as a dinosaur and a bird?

Oculudentavis khaungraae is an ancient small, toothed bird.  The story refers to O. khaungraae as a dinosaur and a bird because it is both; birds are a kind of dinosaur.

2. During what geologic era did O. khaungraae live? Where was it found?

O. khaungraae lived 99 million years ago during the Mesozoic era. The bird’s skull was found in amber in Myanmar.

3. What makes the creature unique?

It is the smallest known dinosaur from the Mesozoic era.

4. What is the length of the creature’s skull? Describe its relative length compared to the average length of a human thumb, which is around 6.6 centimeters.

The creature’s skull is 14.25 millimeters long. The average length of the human thumb, 6.6 cm, converts to 66 mm. So about five skulls lined up would roughly be the same length as a human thumb.

5. What do scientists think O. khaungraae ate during its lifetime? How did they come up with this idea?

Based on the surprising number of teeth found in the bird’s skull, scientists think that O. khaungraae was a predator that may have eaten small fish or invertebrates.

6. What modern animals is O. khaungraae compared to? How is O. khaungraae similar to these animals?

O. khaungraae’s size is comparable to the bee hummingbird, the smallest known bird living today. O. khaungraae’s eye sockets, which are deep and conical in shape, are similar to modern owls.

7. How are O. khaungraae’s eyes different from one of the animals? What could explain this difference?

Though O. khaungraae’s eye socket shape and depth are similar to that of modern owls, the ancient bird’s eyes are positioned on either side of its head, facing outward. An owl’s eyes are positioned on the front of its head. Evolutionary miniaturization — the process whereby animals evolve smaller body sizes — could explain why O. khaungraae’s eyes are side-facing instead of front-facing.  

8. Why might it be hard for scientists to figure out where this ancient bird fits on the tree of life?

Because this bird has a mix of odd features, it is hard to know what birds it is most closely related to.

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